Service Oriented Architecture (SOA)
A service-oriented architecture is essentially a collection of services. These services communicate with each other. The communication can involve either simple data passing or it could involve two or more services coordinating some activity. Some means of connecting services to each other is needed.
A service is a function that is well-defined, self-contained, and does not depend on the context or state of other services
Service-oriented architecture (SOA) is an evolution of distributed computing based on the request/reply design paradigm for synchronous and asynchronous applications. An application’s business logic or individual functions are modularized and presented as services for consumer/client applications. What’s key to these services is their loosely coupled nature; i.e., the service interface is independent of the implementation. Application developers or system integrators can build applications by composing one or more services without knowing the services’ underlying implementations. For example, a service can be implementeZZd either in .Net or J2EE, and the application consuming the service can be on a different platform or language.
he reality in IT enterprises is that infrastructure is heterogeneous across operating systems, applications, system software, and application infrastructure. Some existing applications are used to run current business processes, so starting from scratch to build new infrastructure isn’t an option. Enterprises should quickly respond to business changes with agility; leverage existing investments in applications and application infrastructure to address newer business requirements; support new channels of interactions with customers, partners, and suppliers; and feature an architecture that supports organic business.
SOA with its loosely coupled nature allows enterprises to plug in new services or upgrade existing services in a granular fashion to address the new business requirements, provides the option to make the services consumable across different channels, and exposes the existing enterprise and legacy applications as services, thereby safeguarding existing IT infrastructure investments.
To implement SOA, enterprises need a service architecture, an example of which is shown as below
In Figure above, several service consumers can invoke services by sending messages. These messages are typically transformed and routed by a service bus to an appropriate service implementation. This service architecture can provide a business rules engine that allows business rules to be incorporated in a service or across services. The service architecture also provides a service management infrastructure that manages services and activities like auditing, billing, and logging. In addition, the architecture offers enterprises the flexibility of having agile business processes, better addresses the regulatory requirements and changes individual services without affecting other services.
To run and manage SOA applications, enterprises need an SOA infrastructure that is part of the SOA platform. An SOA infrastructure must support all the relevant standards and required runtime containers. A typical SOA infrastructure looks like Figure 3. The following sections discuss the infrastructure’s individual pieces.
J2EE and .Net
Though the J2EE and .Net platforms are the dominant development platforms for SOA applications, SOA is not by any means limited to these platforms. Platforms such as J2EE not only provide the framework for developers to naturally participate in the SOA, but also, by their inherent nature, bring a mature and proven infrastructure for scalability, reliability, availability, and performance to the SOA world.
Newer specifications such as Java API for XML Binding (JAXB), used for mapping XML documents to Java classes, Java API for XML Registry (JAXR), used for interacting with the UDDI registries in a standard manner, and Java API for XML-based Remote Procedure Call (XML-RPC), used for invoking remote services in J2EE 1.4 facilitate the development and deployment of Web services that are portable across standard J2EE containers, while simultaneously interoperating with services across other platforms such as .Net.
Benefits of SOA
While the SOA concept is fundamentally not new, SOA differs from existing distributed technologies in that most vendors accept it and have an application or platform suite that enables SOA. SOA, with a ubiquitous set of standards, brings better reusability of existing assets or investments in the enterprise and lets you create applications that can be built on top of new and existing applications. SOA enables changes to applications while keeping clients or service consumers isolated from evolutionary changes that happen in the service implementation.
SOA enables upgrading individual services or services consumers; it is not necessary to completely rewrite an application or keep an existing system that no longer addresses the new business requirements. Finally, SOA provides enterprises better flexibility in building applications and business processes in an agile manner by leveraging existing application infrastructure to compose new services.